structure of skeletal muscle.ppt.pptx

Skeletal muscle is one of the three significant muscle tissues in the human body. Each skeletal muscle consists of thousands of muscle fibers wrapped together by connective tissue sheaths. The individual bundles of muscle fibers in a skeletal muscle are known as fasciculi.

1. Structure and Function of Skeletal Muscle Presented By. Vijay Salvekar Associate Professor Dept. of Pharmacology GRY Institute of Pharmacy,borawan

2. Skeletal Muscle Human body contains over 400 skeletal muscles 40-50% of total body weight Functions of skeletal muscle Force production for locomotion and breathing Force production for postural support Heat production during cold stress

3. Structure of Skeletal Muscle: Connective Tissue Covering Epimysium Surrounds entire muscle Perimysium Surrounds bundles of muscle fibers Fascicles Endomysium Surrounds individual muscle fibers

4. Structure of Skeletal Muscle: Microstructure Sarcolemma Muscle cell membrane Myofibrils Threadlike strands within muscle fibers Actin (thin filament) Troponin Tropomyosin Myosin (thick filament)

5. Structure of Skeletal Muscle: The Sarcomere Further divisions of myofibrils Z-line A-band I-band Within the sarcoplasm Sarcoplasmic reticulum Storage sites for calcium Transverse tubules

6. The Neuromuscular Junction Site where motor neuron meets the muscle fiber Separated by gap called the neuromuscular cleft Motor end plate Pocket formed around motor neuron by sarcolemma Acetylcholine is released from the motor neuron Causes an end-plate potential (EPP) Depolarization of muscle fiber

7. Illustration of the Neuromuscular Junction

8. Motor Unit Single motorneuron & muscle fibers it innervates Eye muscles – 1:1 muscle/nerve ratio Hamstrings – 300:1 muscle/nerve ratio

9. Muscular Contraction The sliding filament model Muscle shortening occurs due to the movement of the actin filament over the myosin filament Formation of cross-bridges between actin and myosin filaments Reduction in the distance between Z-lines of the sarcomere

10. The Sliding Filament Model of Muscle Contraction

11. Cross-Bridge Formation in Muscle Contraction

12. Sliding Filament Theory Rest – uncharged ATP cross-bridge complex Excitation-coupling – charged ATP cross-bridge complex, “turned on” Contraction – actomyosin – ATP > ADP & Pi + energy Recharging – reload cross-bridge with ATP Relaxation – cross-bridges “turned off”

13. Muscle Function All or none law – fiber contracts completely or not at all Muscle strength gradation Multiple motor unit summation – more motor units per unit of time Wave summation – vary frequency of contraction of individual motor units

14. Energy for Muscle Contraction ATP is required for muscle contraction Myosin ATPase breaks down ATP as fiber contracts Sources of ATP Phosphocreatine (PC) Glycolysis Oxidative phosphorylation

15. Sources of ATP for Muscle Contraction

16. Properties of Muscle Fibers Biochemical properties Oxidative capacity Type of ATPase Contractile properties Maximal force production Speed of contraction Muscle fiber efficiency

17. Individual Fiber Types Fast fibers Type IIb fibers Fast-twitch fibers Fast-glycolytic fibers Type IIa fibers Intermediate fibers Fast-oxidative glycolytic fibers Slow fibers Type I fibers Slow-twitch fibers Slow-oxidative fibers

18. Age-Related Changes in Skeletal Muscle Aging is associated with a loss of muscle mass Rate increases after 50 years of age Regular exercise training can improve strength and endurance Cannot completely eliminate the age-related loss in muscle mass

19. Types of Muscle Contraction Isometric Muscle exerts force without changing length Pulling against immovable object Postural muscles Isotonic (dynamic) Concentric Muscle shortens during force production Eccentric Muscle produces force but length increases

20. Isotonic and Isometric Contractions

21. Force Regulation in Muscle Types and number of motor units recruited More motor units = greater force Fast motor units = greater force Initial muscle length “Ideal” length for force generation Nature of the motor units neural stimulation Frequency of stimulation Simple twitch, summation, and tetanus

22. Muscle Spindle

23. Golgi Tendon Organ